Wednesday, 26 July 2017

M20: the fascinating Trifid Nebula

The Universe is awash with objects of rare beauty. Such marvels as to leave you with your mouth wide open every time you look at them, in the knowledge that we humans are so insignificant in comparison. One object in particular that rates very high on the beauty scale, is undoubtedly the bewildering Trifid Nebula (M20). Not only is it an incredible spectacle to behold, but it's also a stunning combination of three different kinds of nebulae. The brightest part, surrounding the conspicuous double star, is an emission nebula. It's a region of intense star formation that's being heated up by the radiation of the hot, young stars embedded in it, up to the point that it starts emitting light on its own. The central star is in fact a sextuple system, of which I was able to discern four members at the "modest" magnification of 190x I used here. No star formation's going on anymore in the immediate vicinity of these stars because they've literally scorched away the surrounding gas cloud. The less bright region below is an enormous reflection nebula, merely reflecting the light of the giant star in its centre. And then there are of course the fascinating dark lanes, which are clouds of dust drifting in the foreground. Interesting to note is that these dark lanes show a bright rim on the side which is illuminated by nearby stars.

The whole complex is estimated to be some 21 light-years across, which is five times the distance from our Sun to Proxima Centauri, the nearest other star, and almost the diameter of the mighty Orion Nebula. The reason why the Trifid appears a lot smaller and less bright is because it lies much further away from us: 5,200 light-years as opposed to merely 1,300 for the Orion Nebula. In all, you could say that the two nebular complexes are very similar in size and they're both giant stellar nurseries. Also in the Trifid Nebula dozens of embryonic stars ("proto-stars") have already been discovered.

Another interesting fact about the Trifid is that it's very young, estimated to be no more than 300.000 years old. This makes it one of the youngest emission nebulae known.